MB Pro Retina w/ Dual 2560x1080 monitors

I have a Macbook Pro w/ Retina display (A1502), running Win 7 on bootcamp.
I also have 2 LG 25UM64 monitors. The optimal resolution for these monitors is 2560x1080. However, so far as I can tell I can only hit this resolution if I'm connected through HDMI, for which the MBPro only has one port. The thunderbolt ports won't go past 1920x1080, and I tried an HDMI to USB adapter without any luck.

I'm wondering if there's a way to get this second monitor to go to full resolution. Hoping someone knows how. Thanks!